pH control strategy testing in a bioreactor

A 5-L bioreactor was set up with an impeller, cooling and heating coils, probes for measuring pH, temperature and dissolved oxygen concentration. The reactor instrumentation was interfaced with a computer via data acquisition hardware. LabVIEW, a graphical programming language was used in all measurement and control programs. The reactor temperature control could be achieved by a conventional proportional-integral (PI) controller. In contrast controlling pH was difficult due to a considerable variation in the slope of the titration curve. A simple PI loop resulted in aggressive pH control actions, causing excessive base addition and likely demise of the microorganisms. In this work synthetic waste water was used for testing control schemes. The Generic Model Control (GMC) and gain-scheduling adaptive control strategies were investigated and compared with a PI control scheme. In these strategies, the rate change of pH was assumed to be a function of residence time, base addition, and pH, allowing the continuous calculation of base added against the pH measured. Some experimental and simulated results are presented for comparison